1. Field of the Invention
This invention relates to vibratory concrete screeds, and more particularly, to vibratory concrete screeds which include a laterally translatable concrete spreading device positioned in front of the screed blade for leveling and distributing plastic concrete before the screed blade engages the concrete.
2. Description of the Prior Art
A concrete screed is a device for simultaneously leveling and finishing the entire width of the surface of freshly poured plastic concrete. In order to achieve greater production rates, modern concrete screeds typically incorporate vibration generating mechanisms for vibrating the screed blade which actually engages, levels and finishes the upper surface of the concrete. Triangular truss concrete screeds incorporating spaced apart front and rear blades have become increasingly popular during the last few years for a number of reasons. A triangular truss screed is strong yet light and can be assembled in a variety of lengths from a plurality of separate, shorter length screed frame sections.
Concrete is typically poured between opposing side forms that also support the ends of the screed. Before the screed can be advanced into the area of freshly poured concrete, several workers with shovels must fill in any low places in the plastic concrete and must redistribute the concrete so that the screed blade will initially engage the plastic concrete surface only approximately slightly above the concrete surface. If the upper surface of the plastic concrete is not properly manually leveled and distributed, an excess amount of concrete will come in contact with the screed blade and will ultimately prevent further forward movement of the screed into the unfinished concrete. These manual prefinishing operations must be accomplished promptly to prevent premature setting of the freshly poured concrete before the screed finishing operation has been completed.
The Bid-Well Division of CMI Corporation of Canton, S. Dak. presently manufactures a spinning tube concrete finishing device that utilizes an elevated support bridge which spans the width of an unfinished concrete surface. See U.S. Pat. No. 4,320,987. A laterally translatable spinning tube finishing device is suspended beneath the elevated bridge and is translated from side to side beneath the bridge by an engine driven hydraulic system that engages and displaces a continuous chain. A large horizontally oriented dual-auger assembly is coupled to the front of the laterally translatable spinning tube finishing device. The two counter rotating augers engage the upper surface of the concrete and both level and distribute plastic concrete as the finishing unit is translated from side to side below the support bridge. After an out and back finishing pass has been completed, the support bridge is moved forward on the concrete side forms to reposition the spinning tube finishing rollers for the next out and back finishing pass. The Bid-Well roller finisher also may include a spud vibrator attachment which can be coupled to the laterally translatable finishing device in front of the auger to consolidate the plastic concrete before contact by the augers. The bridge is supported by four spaced apart corner roller assemblies. Each roller assembly includes a jacking device for independently adjusting each of the four corners of the support bridge. Each roller assembly can be positioned at a variable location along the length of the support bridge to permit the roller assemblies to engage concrete forms having variable spacing. Hydraulic motors drive rollers coupled to selected ones of the roller assemblies in order to translate the Bid-Well roller finisher along the concrete forms.
In the Bid-Well device, finishing is accomplished by interaction of the smooth rotating surface of the paired spinning tubes as they are laterally translated back and forth across the upper surface of the concrete. As explained above, a vibratory concrete screed utilizes either a single or two spaced apart vibrating blades to level and smoothly finish the upper surface of the plastic concrete. The screed is continuously advanced into the unfinished plastic concrete surface. The Bid-Well roller finisher accomplishes its finishing operation by laterally translating a pair of spaced apart spinning tubes beneath an elevated bridge deck while the bridge deck is maintained in a fixed position along the concrete side forms.
The Miller Formless Company of McHenry, Ill. manufactures a 30,000 pound directional paver machine which includes an oscillating screed blade and a variable height strike-off auger. This fixed position auger is oriented parallel to the oscillating screed blade. Rotation of the auger spreads concrete along the width of the screed blade.
U.S. Pat. No. 4,335,976 (Morrison) discloses a triangular truss screed having an engine driven vibratory shaft which extends along the entire length of the screed for imparting vibratory motion to the front and rear screed blades. Morrison further discloses a hydraulically powered winch system which incorporates a hydraulic pump which is belt driven by the rotary motion of the screed vibratory shaft. The two spaced apart hydraulic winches are therefore powered by a single internal combustion engine mounted on the screed frame.
U.S. Pat. No. 3,377,933 (Dale) discloses a winch propelled road laying machine having a reciprocating, rear-mounted screed and a front-mounted spreading auger which spans the distance between the concrete forms.
U.S. Pat. No. 2,583,108 (Lewis) discloses a concrete spreader having two spaced apart spreading augers mounted on a carriage and laterally translatable with respect to the machine frame. A vertical distributing plate is mounted on the carriage between the augers to laterally distribute plastic concrete.
Both the Dale and Lewis patents were cited as references against U.S. Pat. No. 4,320,987 referred to above.